284 THE LOWER PRIMATES 



provide dynamic material for a progressively widening sphere of behavioral 

 performance. 



The physiological substratum of such sensory augmentation may be 

 seen in increments to the vohtional control of manual movements. It is also 

 witnessed in the expansion of coordinative regulation whose structural 

 representation is seen in the close interrelation between the cerebellum and 

 the great fields of sensory perception in the cerel^ral cortex. It is apparent in 

 the progressive development of coordmation lor sunultaneous movements of 

 head, eye and hand, structui^ally indicated by increase in the inferior olivary 

 nucleus. The increment in the oculomotor decussation introduced for binoc- 

 ular and stereoscopic vision renders still more exact those skilled movements 

 made possible through the inllux of new sensory impressions. It leads directly 

 to the upbuilding of more extensive kinesthetic associations. 



The dynamic incentives determining all of this expansion may not yet 

 be discerned with clearness. If, however, some motive were presumed to 

 direct the structural design of this process, its goal might well be that instru- 

 ment with which to dominate the environment most effectively, such for 

 example as the hand. 



